1. Field of the Invention
The present invention relates to a blankmask and method for fabricating a photomask using the same, and more particularly, to a blankmask that can be formed to have a resolution of 32 nm or less and that has a pattern fidelity corresponding to the resolution, and a method of fabricating a photomask using the same.
2. Discussion of Related Art
Today, as the increasingly high integration density of large-scale integrated circuits (ICs) has been accompanied by the need for ever finer circuit patterns, semiconductor microfabrication process technology has emerged as a very important issue. In the case of a highly integrated circuit, circuit wires become finer for low power consumption and high-speed operation, and there is a growing need for a contact hole pattern for an interlayer connection and a circuit arrangement for high integration. In order to satisfy this demand, a technique of recording a finer circuit pattern requires manufacture of a photomask, belonging to the field of lithography.
In lithography, a binary-intensity blankmask using a light-shielding layer, and a phase-shift blankmask using a light-shielding layer and a phase-shift film, have been commercially used in order to improve the resolution of a semiconductor circuit pattern. Recently, a blankmask for a hardmask that includes a hard mask film and a light-shielding layer has been developed.
Conventionally, a blankmask for a hardmask has a structure in which a transparent substrate, a light-shielding layer, a hard mask film, and a resist film are sequentially stacked. A final photomask using the blankmask for a hardmask is obtained by forming a light-shielding layer pattern on a transparent substrate. In this case, the resist film is formed to a predetermined thickness since the resist film has selectivity with respect to a lower hard mask film, and the light-shielding layer has a thickness appropriate to secure a predetermined optical density (O.D.), a surface reflectivity feature, a chemical resistance, and a sufficient process margin for defect repair.
Recently, as patterns have become finer and denser, a photomask is required to be manufactured to have not only a high resolution but also precise critical dimension (CD) mean-to-target (MTT), CD uniformity, CD linearity, and pattern fidelity.
However, the following problems may occur when such a fine pattern is formed using a conventional blankmask for a hardmask.
A first problem is related to the thickness of the resist film. The thinner the resist film is, the higher the resolution of a pattern is. To form the resist film to a thin thickness, a time for etching the lower hard mask film is preferably short. However, when a material of a conventional hard mask film is used to form a high-resolution pattern, the time for etching the hard mask film becomes relatively long. Thus, it is difficult to form the resist film as a thin film. Even if a new material can be used instead, it is actually difficult to select a material that has not only selectivity (dry etch characteristics) with respect to the light-shielding layer below the resist film but also a least CD bias with respect to the light-shielding layer.
A second problem is related to pattern fidelity according to the thickness of the light-shielding layer. The light-shielding layer should have optical characteristics and durability (chemical resistance, exposure resistance, a sufficient defect repair margin, etc.) to manufacture a final photomask or perform wafer printing. Thus, the light-shielding layer is formed to a thick thickness so as to satisfy all of the above characteristics. However, recently, as patterns need to be finer to form high-resolution patterns, the light-shielding layer needs to be formed as a thin film. However, since the light-shielding layer should have not only light-shielding properties (optical density) capable of blocking incident light, but also chemical resistance, exposure resistance, a sufficient defect repair margin, etc., the light-shielding layer is very difficult to form as a thin film.